In most audio amplifiers distortion dominantly originates from the non-linear class AB or B biased elements. Generally the backend power amplifier stages operate in class AB or B mode.
Local feedback can be used to minimize the non-linear nature of the input-output transfer characteristic. To further improve the overall linearity it is known to employ a technique of overall negative feedback which is used to achieve the gain stability requirements.
Feedforward is also employed, and it is to be noted that U.S. Pat. No. 4,379,994 suggests the inclusion of an error-generating device to correct for some characteristics of an amplifier, based upon a feedforward circuit and another amplifier. The errors involved, however, are the gross noise and distortion components for which typical compensating networks suffice as the error generator, and not the inherent internal non-linearities of elements themselves.
U.S. Pat. No. 4,549,146 shows a system and method for compensating for non-linearities in electronic circuits.
The distortion effects introduced in a complex multifrequency wave by parametric variations in individual active elements arising from signal and power supply variations in a circuit, such as an audio amplifier, are compensated through the use of replicas of the active elements, and the generation of a feedback signal incorporating comparable distortion. By high gain amplification of the feedback signal in a differential amplifier receiving an input signal that is not comparably distorted a comparison signal is derived containing distortion components. The comparison signal is used in a feedforward path which includes the circuit that is subjected to parametric variations in a sense to cancel the introduced distortions.
The literature shows further power amplifiers with some kind of feedforward distortion compensation. Such power amplifiers are known from    “Feedforward Amplifiers Incorporate Parallel Output Summing”, Danyuk, IEEE transactions on Circuits and Systems I, Vol. 41, No. 12, December 1994;    “Design and Construction of a Feedforward Error-Correction Amplifier”, Takahashi, J. Audio Eng. Soc. Col. 29, No 1/2, January/February 1981,    “Feedforward Error Correction in Power Amplifiers”, Vanderkooy, J. Audio Eng. Soc. Vol. 28, No. 1/2, January/February 1980.
A common disadvantage of the presented power amplifiers with feedforward distortion compensation is the amount of circuitry required for the compensation.
Another common disadvantage is that the compensation is accurate for only one type of load. Though, for example with audio amplifiers, it's important that they can be used with a wide range of loads (such that a single chip can cover a wide market range).